Alloy steel



Patented Feb. 26,1946

Luciano G. Selmi, Detroit, a'mlClarence L. Altenburger, .Dearborn, Mich., assignors to National Steel Corporation, a corporation of Delaware No Drawing. Application September 30, 1942,

Serial No. 460,272

2 Claims. (01.75-126) This invention relates to improvements in low alloy steels. More particularly, the invention re lates to steels of the type disclosed and claimed inlaizplicants Patent No. 2,234,130 issued March In the steels described in the foregoing patent, zirconium is incorporatedas a constituent to deoxidize the steel and attain an inherentlyfine grain. In the present invention,'bysubstituting vanadium for the m'rconium in similar steels the many advantages of the steels of the patent liave been retained while eliminating certain disadvantages inherent in the use of zirconium. These disadvantages in the use of zirconium in no Way afl'ect the characteristics of the patented steels the finished material are the main variables atfecting this condition.

In the specific case of those steels which have become known to the trade as low-alloy high tensile steels, in general they arerequired to possess tensile properties approximately as follows:

Yield point ..p. s. i. min 50,000 Tensile strength do 70,000 Per cent elongationin 2" ..per cent min 25 Many comparatively simple analyses are capable of producing tensile properties in the aforesaid range when rolled hot to comparatively thin but appear only during the manufacture. By the present -invention a similar steel incorporating the same characteristics as those of the patented steels can be more easily produced, the substitu- I tion of vanadium for the zirconium eliminating many of the pouring and casting troubles en-' countered with the use of zirconium. On the other hand, incorporation of the vanadium in place of the zirconium does not deleteriously affeet the physical characteristics of the specific steel involved. Thus the steel of the present invention has substantially the same physical characteristics as the steels disclosed in Patent No.

Objects of the invention include the provision of an improved high tensile steel; the provision of gauges, by controlling finishing temperatures and by the use of copious application of water to the steel on the run out table or cooling bed after the steel has passed through the last stand oi rolls. When the gauge or thickness of strip or. plate, for example,'increases, such procedures become. rapidly less efiective and tensile properties lower than the above minima are obtained from 4 the steel in its rolledcondition.

an improved high tensile steel having a. maximum of 0.25% molybdenum and 0.20% vanadium; and the provision of an improved high tensilelsteel having a maximum of 0.25% carbon.

Other objects or the invention include a pro vision for a steel whose compositionshall be variable within definite ranges in accordance with the size and shape of the finished steel; the proj vision of an improved high tensile steel capable of being heat treated to predetermined but narrow ranges of hardness distribution or other physical properties dependent thereon.

The above being among the objects of the pres ent invention, the same consists in a certain new and useful alloy steel and particularly to one of new and novel analysis as well as to articles formed therefrom whereby to impart to the same certain desirable characteristics, to be hereinafter described and then claimed, having the above and other objects in view.

Asis well known, many compositions of steel 7 produced with laboratoryfacilities can be balanced chemically so as to produce physical prop-ef erties within a given range. Such compositions mayror may not be capable of yielding these same desired properties when subjected to the conditions prevailing in actual commercial steel manufacturing. Rolling'temperatures, rate of cooling 7 after rolling together with the sizeand shape of.

In the past fewwears the requirements of low alloy high tensile steels have increased swiftly. They were originally intended for relatively simple fabrication methods. Today such steels must weld by all commercial welding processes as easily as mild carbon steels; they must be equal to or better than mild carbon steels in the matter of deep drawing objects therefrom; they must be capable of respondingto the ordinary methods of heat treatment and case hardening; they must possess good notched bar resistance at both normaland sub-normal temperatures, high fatigue resistance, especially fatigue resistance at notches or other stress-raisers which may reside within the body of the steel itself. The steel should'have all contained nitrogen fixed in inactive forms and be free from strain .or quenchaging. The steel must not be air hardened at any carbon content and should possess no precipitable elements cap'able of impairing its physical properties upon stress relieving after welding or normalizing. This imposing'list of properties demanded byv ing precision of modern manufacturing and partly. vto 'the increased use o'f'technical testing of fabricatedstructures.

. .Asteel, which will hereinafter be referred to as The balance is iron and incidental impurities.

modern steel users is ,due in part to the increas-- .steel A, of the following analysis has been found The permissible rolling temperatures are, however, quite narrow on the thinner gauges. On

the heavier gauges the cooling rate is too slow to obtain the desired tensile properties in the finished material. Moreover the hardenability of the steel is too low to make heat treatment by quenching and drawing effective for many purin the steel above mentioned but containing, in

addition thereto, small amounts of molybdenum. In other words a steel according to the present invention will have the following composition:

. Per cent Carbon .05- .25 Manganese -5 .50-l..00 Silicon .50- .90 Chromium .25- .75 Vanadium .01 .20 Molybdenum .02- .25 Phosphorus, maximum .03 Sulphur, maximum :03

It is to be understood that although steel A does not equal the performance of steel "B under the conditions set out herein, there are many conditions under which steel A meets all requirements for a highly desirablelow alloy steel.

Nickel and copper may be present as residualv elements. That is, they may be present in the final steel because of forming an alloying element of the steel scrap employed inthe production of the steel of the present invention. Where present as residuals nickel may be present in amounts up to approximately 0.10% and copper in amounts up to approximately 0.14%. Amounts of nickel up to 0.6% and copper up to 0.3% may occur in the alloy of the resent invention without materially affecting theproperties thereof, the nickel in the higher amounts perhaps adding some toughness, enhancing the heat treatment and reduction of area to aslight extent, andadding somewhat to the corrosion resisting properties of the alloy. p

In the matter of carburizing, it has been found that the case strength after heat treating of both steel A and steel B to compare with the highest types of alloy steels for carburizing known to the trade. The core hardness is too low for many purposes in steel A" but steel B, due

toits greater hardenability, corrects this condition.

In the specific case of armor plate applications, this'is a matter of paramount importance. In such applications, one face of the steel plate to be fabricated into armor plate is carburized. Thereafter, the plate is heat treated. It is required that the face not carburized be not too hard for in that event a bullet striking the carburized side may effect cracking on the other side and throw splinters or particles off therefrom defeating the purpose of such armor. 0n the other hand, if the material of the plate in regions not carburized be too soft the case will spell off when struck by a bullet and hence render that area liable to penetration upon being struck by a second bullet thus defeating the purpose of the armor. I

When utilizing steel "B" in heat treated plates,

' various optimum percentages of the constituents have been found to exist. The following table shows these preferred compositions? Thickness of plate (inches) Under )4 M to 1 2 and up Per cent carbon 0. 15-0. 25 0. 15-0. 25 0. 15-0. 25 Per cent manganese 50- 75 .85- 95 .90-1. 00 Per cent silicon .50- .90 .50 .90 .60- .90 Per cent chromium..- 50- 75 .70 .60 Per cent molybdenum. .10- 20 l0- 20 10-. 20 Per cent vanadium Oll0 01- 10 01- 10 The steel of the present invention is inherently fine grained and substantially deoxidized.

From the foregoing description it will be seen that the applicants have produced a low alloy high tensile steel having its alloyelements selected, combined and balanced within narrow, but specific and critical ranges, whereby the improved steel having the characteristics and accomplishing the objects set forth is provided.

We claim:

1.A low alloy high tensile steel having deep drawing properties, high fatigue resistance and freedom from strain and'quench aging, consisting of carbon .05 to 35%; manganese .85 to 1.00%; silicon .50 to .90%; chromium .50 to 35%; vanadium .01 to .10%; molybdenum .02 to 25%; the balance being iron and incidental impurities.

2. A low alloy high tensile steel having deep drawing properties, high fatigue resistance and freedom from strain and quench aging, consisting of carbon .15 to 25%; manganese .85 to 1.00%; silicon .50 to-.90%; chromium .60 to 30%; vanadium .01 to 210%; molybdenum .10 to 20%; the balance being iron and incidental impurities. 

